export type TaskHandler<T> = () => T | PromiseLike<T>

export type Queue<T> = {
    push: (task: TaskHandler<T>) => Promise<T>
    readonly length: number
}

export const makeTaskQueue = <T,>(): Queue<T> => {
    let pending: Promise<T | void> = Promise.resolve()
    let count: number = 0

    const run = async (task?: TaskHandler<T>) => {
        count++
        try {
            await pending;
        } finally {
            count--
            return Promise.resolve().then(task);
        }
    }

    return {
        push: (task: TaskHandler<T>) => pending = run(task),
        length: count,
    }
}

export default makeTaskQueue